Belt-type presses for making particleboard, fiberboard, copper clad boards for printed circuit boards and the like are known in the prior art related to the invention. The materials being pressed (known as press materials or press products) can include laminates, rubber products, particleboard, plastics and any other products formed by pressing multiple layers together. Generally, belt presses comprise an endless upper press belt, often a steel press belt, circulated over spaced-apart guide belt rollers, and a corresponding endless lower press belt, also often a steel press belt, circulated over spaced-apart guide belt rollers as well. Between them, these press belts form a pressing gap or pressing region of the belt-type press, between the press framework having upper and lower platens. The upper and lower belts each have their own drive mechanisms. In a known press of this type, two chains are associated with each of the press platens and press belts, or a total of four chains per belt press system. The upper and lower platens form an entrance region along a complete horizontal plane.
Into the pressing region between the platens and their corresponding press belts, the spaced apart rollers are fed and guided along a circulation path with the aid of upper and lower roller circulation mechanisms. The roller circulation mechanisms comprise upper and lower chain sets, where each set is driven by a chain drive sprocket. The chain sets, in turn, circulate or drive the rollers so that the rollers move along with the press belts, situated between their respective belts and the platens. Guide rails are used to channel the movement of the chain sets and rollers in the intended direction. Thus, the upper press mechanism has two chains with rollers disposed across the width of the press between both chains, and the lower press mechanism has two corresponding chains with rollers disposed between them as well.
In many cases, the upper and lower platens are heated. The rollers are situated between the steel press belts and the heated platens. The rollers are equally spaced apart and roll more or less along with the belt. As press material is inserted into the entrance of the pressing region (or press gap entrance), the steel press belts are contacted by the press products on one side and the rollers on the other. In turn, the rollers contact the press belts and the heated platens, thus acting to transfer heat from the platens to the steel belts. The heat is ultimately transferred from the platen to the steel press belt via the rollers. Finally, the heat is transferred from the steel press belt to the press material.
For the circulation of rolling rods to the press gap entrance, the rolling rods are channeled along guide rails and links cooperating with sliding wheels and guide wheels. Both sets of chains, that is, the upper and lower chain sets, are driven individually by chain drive motors. Each motor is connected to a chain drive axis, which has chain drive sprockets disposed at its ends. The upper and lower chain drive systems, however, are not connected mechanically because the belt press is specifically designed to open. That is, the upper and lower belt press mechanisms form a "C", with the upper belt press as the top half of the "C", and the lower belt press as the bottom half. In this manner, the belt press system can easily be maintained, and all moving parts are freely accessible to the operator or maintenance personnel.
Since the upper and lower roller chain drive mechanisms are not mechanically connected, problems result when the relative positions of the upper and lower chain/roller mechanisms cannot be accurately synchronized. That is, the rollers may travel at different speeds, resulting in a condition where the upper and lower roller sets occasionally overlap. In normal operation, the upper and lower roller sets are equally spaced apart and staggered from top to bottom so that either an upper or lower roller is aligned with and reach the press gap entrance at a time, but never both simultaneously. For example, when an upper press roller is at the press gap entrance, a space between two rollers of the lower press should be aligned at that same point. In this manner, only one roller (either an upper or lower roller) is contacting its press belt at the press gap entrance at a time. However, in the absence of any mechanism to keep the upper and lower roller chains synchronized, the upper and lower roller chains "drift" with respect to each other, and the upper and lower rollers eventually overlap at the press gap entrance. That is, an upper roller and lower roller can reach the press gap entrance at exactly the same moment. When this occurs, the press material is "pinched" between the two rollers, and a press material defect known as a bar mark occurs. Bar marks are the result of the roller overlap at the press gap entrance, and are created by high localized pressure loading. It is a primary objective for a belt press to fabricate press material without defects caused by bar marks. One solution to this problem would be to use a single interconnected drive mechanism for both the upper and lower roller sets, by connecting the upper and lower chain drive axes with, for example, a timing chain. That technique, however, makes separation of the upper and lower presses difficult, which hinders maintenance and overall press versatility.